Cathode sheet for electrodeposition and method of recovering electrodeposited metals

ABSTRACT

A cathode sheet of titanium for use in an electrodeposition process for metals, such as copper, and a method of recovering the metal. The sheet is thin and its width tapers in the downward direction. After a deposit of the metal has built up on both faces and around the side and bottom edges of the sheet, the sheet and deposit are taken from the electrodeposition apparatus. The deposit is heated to expand it to a greater extent than the sheet, allowing the deposit to be slipped off readily.

United States Patent n91 Bomberger, Jr.

[451 Dec. 18,1973

1,694,962 12/1928 Berry 204/281 FOREIGN PATENTS OR APPLICATIONS 4,499 1885 Great Britain 204/9 Primary Examiner-T. M. Tufariello Attorney-Walter P. Wood [5 7] ABSTRACT A cathode sheet of titanium for use in an electrodeposition process for metals, such as copper, and a method of recovering the metal. The sheet is thin and its width tapers in the downward direction. After a deposit of the metal has built up on both faces and around the side and bottom edges of the sheet, the sheet and deposit are taken from the electrodeposition apparatus. The deposit is heated to expand it to a greater extent than the sheet, allowing the deposit to be slipped off readily.

11 Claims, Drawing Figures PATENTEDHEB 18 ms FIG. 3.

v FIG. 2.

CATHODIE SHEET FOR ELECTRODEPOSHTION AND METHOD 01F RECOVERING ELECTRODEPOSIITED METALS This invention relates to an improved cathode sheet for use in electrodeposition of metals, and to an improved method of recovering electrodeposited metals. Although my invention is not limited to use with any overvoltage material, such as a metal of the platinum specific metal, my cathode sheet and method are par- 1 ticularly useful in electrowinning and electrorefining processes for copper. The conventional practice in such processes is to employ thin copper starter sheets, about 0.020 to 0.050 inch thick, as cathodes. Copper is electrodeposited on these sheets to a thickness of about five-eighths inch, after which the sheets with the deposits thereon are removed from the deposition tanks for further processing. Typical operating conditions are stated in table form hereinafter. This practice necessitates the use of new copper starter sheets to form every deposit. Preparation of the starter sheets is a costly operation.

It is known that copper and other metals, including manganese, zinc, gold, silver, lead and chromium, can be deposited readily on titanium sheets as cathodes. Thin copper deposits are readily separated by stripping and peeling from the titanium surface. In fact, such copper deposits are of such high quality and are removed so readily that titanium sheets are being evaluated as cathodes for growing copper starter sheets, which in turn are used in the conventional practice. Unfortunately thick deposits of copper are not readily separated from titanium cathode sheets because copper which deposits on the edges, as well as on faces, adheres firmly as an envelop to the titanium. One method which has been considered for overcoming this problem is to mask the edges of the titanium sheet. This arrangement has not worked well for the reasonthat electrodeposition of copper, and handling, damage the edge strips, and they must be replaced frequently. As used herein, the term titanium" refers to the various titanium-base alloys, as well as the unalloyed metal.

An object of the present invention is to provide an improved titanium cathode sheet which enables a thick deposit of another metal to build up on the sheet, yet permits easy separation.

A further object is to provide an improved method of recovering metals, such as copper, by electrodeposition on a titanium cathode sheet, and separated readily as a thick deposit in condition for subsequent processing.

In the drawing:

FIG. l is a diagrammatic sectional view of an electrodeposition apparatus in which the cathodes are sheets constructed in accordance with my invention;

FIG. 2 is a vertical section on lines Il-Il of FIG. 1;

and

FIG. 3 is an exploded side elevational view of the cathode sheet and deposit.

FIG. 1 shows an electrodeposition apparatus which is conventional apart from my novel cathode sheet. The apparatus comprises a tank which contains an electrolyte providing ions of the metal to be deposited, anodes 13, and titanium cathode sheets 13 formed in accordance with my invention. In an electrorefining process, the anodes are formed of the same metal as that deposited in the process, for example, copper. In an electrowinning process, an anode of an essentially insoluble material is used. Examples of the latter materials are graphite, lead, and titanium coated with a low Typical Conditions Refining Winning Copper, g/I 44 to 50 20 to 50 Free H,so, /1 170 to 210 m 125 Temperature, "C 55 to 65 30 to S0 Ampers/sq ft of cathode 15 to 20 I3 to 20 Voltage drop 0.2 to 0.35 2.0 Anodes 99 Cu Pb-Sb-Ag-alloy Cathode starter sheets Copper Copper In accordance with my invention, the width of the titanium cathode sheet'13 tapers in the downward direction. Each side edge 19 of the sheet lies at an angle of about 5 to l5 to the vertical. Ideally the thickness of the sheet also tapers at an angle of up to about 5 in the downward direction, but I have discovered this is not essential, and the sheet may have a uniform thickness of about 0.1 inch. Greater tapering than necessary for stripping reduces efficiency. To prevent a deposit 20 from dropping off the cathode sheet prematurely, I may make one or more small holes 22 (about one-eighth inch) through thesheet near the upper edge. During the deposition process, small slugs of metal are electrodeposited in these holes and form supporting members which connect the deposits on opposite sides of the sheet.

After a deposit 20 of copper or other metal has built up to the desired thickness on both faces of the sheet 13 and around the side and bottom edges, I remove the sheet and depositfrom the electrodeposition apparatus. Typically the sheet carries a deposit on each side about 0.25 to 1 inch thick when taken from the apparatus. The deposit is readily separated from the sheet. In the example of copper, the sheet and deposit typically are at a temperature of about 40 to 60C as taken from the apparatus. I beat the deposit to a temperature about 25 to 300C above this temperature. Conveniently, I may use steam jets for this purpose. The coefficient of linear expansion of titanium is about 8.5 X l0 /degree C which is lower than the coefficient of the deposited metal, about 16.6 X l0 /degree C in the example of copper. Consequently heating the deposit expands it to a greater extent than the titanium cathode sheet and enables it to be slipped off the sheet. The optional supporting slugs which lie within holes 22 shear off with light vibration or jolting. After the metal deposits are removed, the titanium sheets are reused and the process repeated. The deposits are washed with water and dried for subsequent processing. Since the deposits are in the form of envelopes, washing is facilitated by cutting them apart or by expanding the openings.

costly starter sheets conventionally employed in the copper industry.

I claim:

1. A titanium sheet for use as a cathode in electrodeposition of metals, the width of said sheet tapering downwardly throughout the area on which metal is to be deposited with each side edge of the sheet lying at an angle of about 5 to to the vertical, said sheet being constructed to be suspended from its upper edge in an electrodeposition apparatus, whereby a deposit can build up on both faces and around the side and bottom edges of said sheet and be readily separated therefrom in the form of an envelope when the sheet and deposit are taken from the apparatus.

2. A sheet as defined in claim 1 in which said sheet has at least one hole near its upper edge within which a slug of metal can be deposited to prevent the deposit from dropping off the cathode prematurely.

3. A sheet as defined in claim 1 in which the thickness also tapers in the downward direction.

4. The combination, with an apparatus for electrodeposition of metal, which apparatus includes a tank, and anodes suspended in said tank, said tank being adapted to contain an electrolyte providing ions of the metal undergoing deposition, of cathode sheets suspended in said tank on which the metal is deposited, said sheets being constructed as defined in claim 1.

5. A combination as defined in claim 4 in which said anodes are of the metal undergoing deposition.

6. A combination as defined in claim 4 in which said anodes are of an essentially insoluble material of the group consisting of graphite, lead and titanium coated with a low-overvoltage material.

7. In an electrodeposition process for metals, wherein a metal is deposited on a cathode sheet, an improved method of recovering said metal, said method comprising supporting a cathode sheet in the electrodeposition apparatus, said sheet being of titanium and tapering in width in the downward direction throughout the area in which metal is to be deposited, depositing metal on said sheet until a deposit of the desired thickness has built up on each face thereof and around the side and bottom edges, taking the sheet and deposit from the apparatus, heating the deposit to a temperature about 50 to 300C higher than the temperature at which it is taken from the apparatus, and slipping said deposit from said sheet in the form of an envelope.

8. A method as defined in claim 7 in which said metal is copper.

9. A method as defined in claim 7 in which the thickness of the deposit on each side of the sheet is about 0.25 to 1 inch.

10. A method as defined in claim 7 in which said sheet has at least one hole near its upper edge and a slug of metal is deposited in said hole to prevent said deposit from dropping off said sheet prematurely.

11. A method as defined in claim 7 in which removal of said deposit is aided by an applied force including vibration and jolting. 

2. A sheet as defined in claim 1 in which said sheet has at least one hole near its upper edge within which a slug of metal can be deposited to prevent the deposit from dropping off the cathode prematurely.
 3. A sheet as defined in claim 1 in which the thickness also tapers in the downward direction.
 4. The combination, with an apparatus for electrodeposition of metal, which apparatus includes a tank, and anodes suspended in said tank, said tank being adapted to contain an electrolyte providing ions of the metal undergoing deposition, of cathode sheets suspended in said tank on which the metal is deposited, said sheets being constructed as defined in claim
 1. 5. A combination as defined in claim 4 in which said anodes are of the metal undergoing deposition.
 6. A combination as defined in claim 4 in which said anodes are of an essentially insoluble material of the group consisting of graphite, lead and titanium coated with a low-overvoltage material.
 7. In an electrodeposition process for metals, wherein a metal is deposited on a cathode sheet, an improved method of recovering said metal, said method comprising supporting a cathode sheet in the electrodeposition apparatus, said sheet being of titanium and tapering in width in the downward direction throughout the area in which metal is to be deposited, depositing metal on said sheet until a deposit of the desired thickness has built up on each face thereof and around the side and bottom edges, taking the sheet and deposit from the apparatus, heating the deposit to a temperature about 50* to 300*C higher than the temperature at which it is taken from the apparatus, and slipping said deposit from said sheet in the form of an envelope.
 8. A method as defined in claim 7 in which said metal is copper.
 9. A method as defined in claim 7 in which the thickness of the deposit on each side of the sheet is about 0.25 to 1 inch.
 10. A method as defined in claim 7 in which said sheet has at least one hole near its upper edge and a slug of metal is deposited in said hole to prevent said deposit from dropping off said sheet prematurely.
 11. A method as defined in claim 7 in which removal of said deposit is aided by an applied force including vibration and jolting. 